Filtration device and process for its manufacture

ABSTRACT

Disclosed is a process for manufacturing a filtration device. The process includes a fiber carding procedure which forms a web. The filtration device in accordance with the invention takes the form of a web consisting of a single layer lap.

[0001] The present invention concerns a process for manufacturing afiltration device more particularly intended for filtering gases such asair for ventilating and/or heating and/or air conditioning rooms ormotor vehicles.

[0002] The invention also concerns a filtration device manufactured bythe above process.

[0003] Prior art filtration devices are made by spinning athermoplastics polymer through nozzles to produce an intermingling ofthe filaments issuing from the nozzles forming, after cooling, a lapthat can constitute a particle filter.

[0004] The prior art processes have the drawback of necessitating thesuperposition and binding together of a plurality of layers in order toobtain filters that are sufficiently efficient.

[0005] The filters obtained in this way have a high specific gravity anda high unit cost.

[0006] An aim of the invention is to manufacture a filtration devicethat is efficient and less dense and more economic than the prior artdevices.

[0007] The process for manufacturing a filtration device of theaforementioned type in accordance with the invention is characterised inthat it comprises an operation of carding fibres having a length in therange 38 mm to 120 mm and a diameter greater than 10 μm to form anisotropic web and in that said web is subjected to a mechanicalconsolidation operation by means of hydraulic binding consisting inpassing very fine water jets at a high pressure through the web disposedon a rotating drum followed by a drying operation.

[0008] In accordance with other features of the process in accordancewith the invention, separately or in all technically possiblecombinations:

[0009] the carding operation is carried out using a wool type card;

[0010] said card incorporates “Dispelmel” type randomising units;

[0011] the pressure of the water jets used for the hydraulic binding isin the range 40 bars to 200 bars;

[0012] the parameters of the card are chosen to obtain a web having amass per unit surface area in the range approximately 20 g/m² toapproximately 150 g/m².

[0013] In accordance with the invention the filtration device of theabove type is characterised in that it comprises an isotropic web.

[0014] In accordance with other features of the filtration device inaccordance with the invention, separately or in all technically possiblecombinations:

[0015] said web is in a single layer;

[0016] the length of said fibres is at least equal to 38 mm;

[0017] the length of said fibres is at most equal to 120 mm;

[0018] the average diameter of said fibres is at least equal to 10 μm;

[0019] said fibres are fibres of the same kind or a mixture of differentfibres.

[0020] said fibres are selected from the group of thermoplastics fibressuch as fibres of polypropylene, polyethylene, polyester, polycarbonate,polyamide, the group of acrylic fibres, pre-oxidised acrylic fibres, thegroup of aramide fibres, the group of phenolic fibres, the group offluorocarbon fibres, the group of mineral fibres such as glass fibresand the group of metal fibres.

[0021] It has been found that the invention provides a filtration devicethat is efficient and of lower unit cost and of lower specific gravitythan the prior art filtration devices.

[0022] Another important advantage compared to the prior art is that thehead loss when a gas passes through the filtration device is much lower.

[0023] Other aspects and advantages of the invention will becomeapparent in the following description of one embodiment of a filtrationdevice designed to be installed in equipment for heating/airconditioning a motor vehicle.

[0024] 1.7 Tex (14 μm diameter) polypropylene fibres are cut to a lengthof 40 mm and then introduced into a mixer.

[0025] The fibre mixture obtained is then carded by means of atwo-doffer wool type card equipped with a “Dispelmel” type randomisingunit to obtain an isotropic web.

[0026] In one variant of the process the web leaving the card isintroduced into a condenser to form a single layer lap.

[0027] The parameters of the card and/or of the condenser are selectedto produce a web or a lap having a mass per unit surface area in therange approximately 20 g/m² to approximately 150 g/m².

[0028] The web or lap is deposited onto a belt and then consolidated bya hydraulic binding operation.

[0029] The hydraulic binding operation consists in passing very finewater jets at a high pressure (in the range 40 bars to 200 bars) throughthe web or lap disposed on a rotating drum.

[0030] When they bounce off the drum the water jets cause knotting ofthe fibres imparting a high mechanical strength to the web or lapwithout significantly increasing its specific gravity.

[0031] After drying, the web or lap is mounted on a support to form thefiltration device.

[0032] Using a 0.84 mm thick web or lap the process has produced afilter having a mass per unit surface area of 66 g/m² and a specificgravity of 0.07.

[0033] To test the efficiency of a filter obtained in the above manner,it was disposed across a 100 cm² 20 cm/s flow of air laden withparticles.

[0034] The particles corresponded to a “fine SAE powder” defined in USStandard SAE J 726/ISO 5011.

[0035] The particle concentration was 100 mg/m³.

[0036] The head loss across the filter under the above conditions wasonly 14 Pa and the efficiency was 80%.

[0037] Compared to filtration devices currently on the market, anefficiency comparable to the best of them was obtained with a producthaving a much lower specific gravity (0.07 compared to 0.12 to 0.30)generating a much lower head loss.

[0038] Endurance tests have shown that the efficiency of the filtrationdevice in accordance with the invention is more stable with time.

[0039] What is more, the process described hereinabove is carried outcontinuously and produces the filtration device in a single operation.

1. A process for manufacturing a filtration device more particularly intended for filtering gases such as air for ventilating and/or heating and/or conditioning rooms or automobile vehicles, characterised in that it comprises an operation of carding fibres having a length in the range 38 mm to 120 mm and a diameter greater than 10 μm to form an isotropic web and in that said web is subjected to a mechanical consolidation operation by means of hydraulic binding consisting in passing very fine water jets at a high pressure through the web disposed on a rotating drum followed by a drying operation.
 2. A process according to claim 1 characterised in that the carding operation is carried out using a wool type card.
 3. A process according to claim 2 characterised in that said card incorporates “Dispelmel” type randomising units.
 4. A process according to any one of claims 1 to 3 characterised in that the pressure of the water jets is in the range 40 bars to 200 bars.
 5. A process according to any one of claims 1 to 4 characterised in that the parameters of the card are chosen to obtain a web having a mass per unit surface area in the range approximately 20 g/m² to approximately 150 g/m².
 6. A process according to any one of the preceding claims characterised in that the web is in a single layer.
 7. A process according to any one of the preceding claims characterised in that said fibres are fibres of the same kind or a mixture of different fibres.
 8. A process according to claim 7 characterised in that said fibres are selected from the group of thermoplastics fibres such as fibres of polypropylene, polyethylene, polyester, polycarbonate, polyamide, the group of acrylic fibres, pre-oxidised acrylic fibres, the group of aramide fibres, the group of phenolic fibres, the group of fluorocarbon fibres, the group of mineral fibres such as glass fibres and the group of metal fibres.
 9. A filtration device for filtering gases such as air for ventilating and/or heating and/or air conditioning rooms or motor vehicles manufactured in particular by the process according to any one of the preceding claims characterised in that it consists of an isotropic web.
 10. A filtration device according to claim 9 characterised in that the web is in a single layer.
 11. A filtration device according to claim 9 or claim 10 characterised in that the isotropic web is made up of fibres having a length in the range 38 mm to 120 mm and an average diameter at least equal to 10 μm.
 12. A filtration device according to claim 9 or claim 10 characterised in that the isotropic web is made up of polypropylene fibres having a length in the range 38 mm to 120 mm and an average diameter at least equal to 10 μm. 